Impedance set



June z5, 1935'. L. EHR 2,005,986

IMPEDANCE SET 116k Ff 1? T3 F4. ff

L [TV-*FIL QTLlH- June z5, 1935. 1-EHR 2,005,986

Y IMPEDANCE SET Filed De0.4, 1931 2 Sheets-Sheet 2 -wim o J 1 4 o Patented June 25, 1935 UNITED STATES IMPEDANCE SET Leo Behr, Philadelphia, Pa., assign to Leeds c f Northrup Company, Philadelphia, Pa., a corporation oi' Pennsylvania Application December 4,

8 Claims.

My invention relates to reactance or resistance sets; such as decade sets, for introducing known values o! reactance or resistance into an electrical system, particularly a measuring circuit or net- 5 work.

In accordance with my invention, the number. of resistors or reactors is not only less than the number of possible steps but the arrangement is such that the transition from one setting to the other does not introduce values of resistance or reactance which are outside of the initial and final settings. 4

More specilically equal reactances are connected so that for the maximum setting, their values are additive, i. e., resistances, or in- `ductances, are connected in series, while condensers are connected in parallel, and alternate lesser steps are obtained by progressively excluding the resistances or reactances from circuit. The intermediate values between the alternate steps are obtained by including in circuit with the last active resistor or reactor, an auxiliary resistor or reactor, of such value and in such circuit relation .that the effective value of the last active resistor or reactor is halved.

My invention further resides in the features of combination and arrangement hereinafter described and claimed.

For an understanding of my invention and for illustration of some of the forms it may take, reference is to be had to the accompanying drawings in which:

Figs. 1 to 3 diagrammatically illustrate a resistance box for diierent settings to obtain different resistance values.

Figs. 4 and 5 are top and bottom plan views respectively of a resistance box.

Figs. 6, '7 and 8 are detailed views taken respectively on lines 6-6, 1 1, and 8--8 of Fig. 5.

Fig. 9 is a wiring diagram of the resistance box of Figs. 4 and 5. f

Fig. 10 diagrammatically illustrates a reactance or condenser box. y

Heretofore, in resistance sets in which the nurnber of resistances was less than the number o'l steps or'settings, it was necessary in changing from one setting to the next, either to open a circuit, in which event the effective resistance of 'the box became temporarily infinite, or one or more resistance sections were short-circuited, so

that the value of eiective resistance of the box to the external circuit was lower than both settings. More generally expressed, with the previously knownarrangements, in the transitionV 1931, Serial No. 578,951

from one setting to thel next, there was temporarily introduced into the external circuit a resistance value which lay outside the initial and iinal settings.

Referring to Fig. 1, the resistance sections or units Ri, R2, etc., are connected in series with each other to one terminal T of the set. The resistors are preferably equal in value, and the value of each resistance is double that of the increment of resistance effectedin changing from l0 one setting of the box to the other. The resistances are connected to a series of contacts F, FI, etc. The contacts M and Ml whose relative position remains xed, are adapted successively to engage the series of contacts F to F5, for diierent settings. The contacts M, Ml may be moved, preferably together as a unit, or they may remain fixed, and the contacts F, FI, etc., moved successively into engagement with them.

For simplicity, contacts F to F5 are shown 20 of equal length and equally spaced. Contact IMI is suitably greater in length than the distance a between the adjacent ends ci contacts F, FI, etc. Contact M is suitably shorter than the distance a between the same contacts. The distance between the remote edges of contacts M and Ml should be less than the distance between the centers of any pair of adjacent contacts F, FI, etc.

Particularly for convenience of explanation, the contact plate F6 is shown provided with a. scale corresponding numerically to the resistance settings. For the position of contacts shown in Fig. 1, the resistancesetting is zero, the current entering the terminal T, for example, passing directly to contact F without traversing any of the resistance sections, and then through contact MI to the other terminal TI of the box.

In going to the next higher setting, Fig. 2, the contact MI iirst engages contact Fl and upon further movement and while still in engagement with contact FI, passes out of engagement with contact F, connecting resistance R6 in shunt to resistance RI. Preferably the resistances R6 and RI are of equal magnitude so that the effec- 'tive resistance across the terminals T, Tl is half the value of either of the resistances. In this transition from the zero setting to the next higher, the resistance introduced in the external circuit did not exceed the iinal setting for until resistance R6 was connected in shunt yto resistance RI, it was short circuited by the contact F and as soon as this short circuit was removed by the contact MI passing beyond contact F, resistance R6 was immediately connected 55 in shunt to resistance Rl, so that at no time was the circuit interrupted, or either Rl or R6 alone in circuit.

To increase the setting still further, the contacts M, MI, are again moved to the right, the resistance in the external circuit remaining at the lower value until the trailing edge of contact M passes 01T contact F (Fig. 3) whereupon all of the current at once flows through resistance RI only. Again in the transition, the cir cuit between terminal T, T-l is maintained closed and the resistance changed directly from one value to the next.

For the next higher setting, the contacts M, Ml are further moved to the right to the next zone of the scale. contact M engages contact FI, without effecting any resistance change, since the resistance R6 is short circuited by the engagement of FI with both of the contacts M, Ml. As soon, however, as the contact MI passes beyond the contact F5, the current, all of which flows through resistance RI, divides, part going through resistance R2 and the remainder through resistance R6. The effective resistance in circuit is therefore now the sum of resistance Rl plus half the resistance of either resistance R2 or R6. The change in setting did' not introduce temporarily any value of resistance outside of the third and fourth setting (scale readings v2 and 3) for the resistance RI remained in circuit until contact MI left contactFl and then R6 was immediately connected in shunt to R6 without any circuit interruption, and without effecting any other temporary circuit connection of any of the resistors.

yFrom the foregoing, it is to be understood that for alternate settings, one of the resistance sections Rl, R2, etc., is included or excluded from circuit, while for the intermediate, or every other setting, the resistance R6 is in shunt to the last active section. It is apparent from the fore going that with this arrangementof contacts and resistances the transition from one setting to the next does not introduce any resistance value which lies outside the nal or initial settings.

For a decade set, that is, one having ten steps, of equal value, only six resistors are required, and these as above stated, for equal increments of resistance, are all of an equal value which is twice the increment change. For example, if the set is for varying the resistance from zero to ohms in 10 ohm steps, each `of the resistances RI to R6 will have a value of 20 ohms.

It is further to be noted that in my arrangement the circuit connections and contact arrangement is simple, which permits reliable operation and'affords ease of construction.

In Figs. 4 to 9 there is shown a resistance box utilizing ln series of four arrangements such as have been described, so that the box may be set to obtain Widely varying resistance values, in both large and small steps. Upon each of the rotatable drums I to 4, are mounted a group of resistors connected in series, each group corresponding to the resistances Rl to R5 of Fig. 1, the resistors of the several groups having different Values. The resistors are preferably of the woven type and mounted on cylindrical forms as more clearly shown and claimed in copending Tarpley application Serial No. 586,518, filed January 14, 1932, which hasl since issued as Patent 1,992,499, Sept. 4, 1934. The contacts FI to F5connected to the resistances, are carried by the drum and successively engage the xed contacts M, Ml, as

During this movement, the

aooaeee the drum is rotated by a knob which can be manipulated from the exterior of the housing or box to change the resistance settings. v

A brush B engages the terminal contact 5 at the center of each drum which is connected to oontact F and corresponding end of resistance Rl. The bracket or support 6 for holding the brush B, is held to the top panel 1 by the binding posts or terminals T, TI, as most clearly shown in Fig. 6. Each of theA remaining brackets 1, each of which carries a pair of contacts M, M, is provided with a recess or opening 8 in which a resistance R6 is disposed. 'Ihe connections to the several contacts M, M l and brushes B are most clearly shown in Fig. 9. l

The mountingv of the main resistors upon the drums is of material advantage as it not only reduces the cost of construction, but increases the dcpendability by greatly reducing the number of sliding contacts and the number of joints in the electrical path between the groups of resistors. With the construction shown, the conductors and brushes carrying current to thev resistors remain in the same position.

By way of example only, the dial K! (Fig. 4)

may be for adjusting the resistance from zero to 10,000 ohms in steps o 1000 ohms, in which case the resistances Ri to R6 of the rst section of the box would each have a value of 2000 ohms;` the dial K2 is for adjusting the resistance of the second section from zero to 1000 ohms in 100 ohm steps, and the resistances Rl to R6 of that section will each have a value of 200 ohms; similarly the knob K3 may be for` adjusting the resistance of the third section from zero to 100 ohms in 10 ohm steps, in which case the resistance RI to R8 will each have a value of 20 ohms; and theV dial K4 may be for adjusting the resistance from zero to 10 ohms in 1 ohm steps. in which case each of the resistances RI to R6 will have a value of two ohms. In this box, using only 24 resistances, the resistance introduced into the external circuit may be varied from zero to'11,l10, by l ohm steps if desired, and throughout this range a transition in any one dial from one setting to the next does not introduce into the external circuit any resistance value which is outside of the initial and final setting, and more specically for a change in setting the resistance changes directly from one value to another. Notches in the. bottom Iianges of the drums engage a spring-pawl or equivalent click deviceto ensure proper relation of contacts M and MI with respect to contacts F to F5 for the eleven positions of each drum.

It is also a characteristic of the arrangement shown that the inductive and capacity eiects are minimized. For example, the connection from terminal TI of the box to the brush M of the lowest resistance group on drum 4 is made by wires W and WI, connected in parallel. These wires, as shown in Fig. 5. pass on opposite sides of the two brushes B, MI between drums 2, 3 and 4. and as the current flow through them is in a direction opposite to the current flow through the brushes, the inductive effects are substantially annulled. To minimize capacity eiects, .the conductors W, WI` are substantially spaced from the resistors of drum I and associated conductors, which are of materially dierent potential.

While l have described my invention as specifically applied to resistance boxes, t'he same principles may be utilized for reactance boxes, that is, in which inductance or capacity is changed by incremental steps. The connections` and switching arrangement for inductances are the same as for resistance. Precaution should be taken to avoid coupling between the inductances, i. e. the inductances should be so posltioned or so shielded that there is zero or insubstantial interlinkage of their fields.

Since capacities are additive when connected in shunt instead of being additive when connected in series, as is the case with inductances and resistances, a modication of the connections and contact arrangement is made. Fig. l illustrates a decade set, affording l0 equal steps of capacity by using only six condensers, and is characterized by the fact that in changing from one setting to another there is not introduced into the external circuit any capacity which is beyond the initial and final settings.

The condensers CI, C2, etc., each have one terminal connected to a conductor 9 extending to terminal post T. The other terminals of the condensers are connected respectively to contacts FI to F5. At the setting for maximum capacity, all of these contacts are engaged by the contact m, so that the condensers Cl to C are all connected in parallel across the binding posts T, Tl. For the next lower setting, the contact m engages only contacts Fl to F4, and the contact ml engages contact F5 to connect the condenser C6 in series with condenser C5. As the condensers CI to C6 are of equal value, the eiective capacity of C5 in series with C6 is only half the value of either. The total capacity for this setting is therefore equal to the sum of the capacities of condensers CI to C4 plus half the capacity of condenser C5. For the next lower setting, the contact m continues to engage contacts FI to F4, but the contact mi moves to a position intermediate contacts F4 and F5, so that there is included in circuit only the condensers Cl to C4.

Accordingly, as the contacts m, ml move to the left, the condensers C4 to CI are successively excluded from circuit for each second movement of the contacts, while for every other movement or intermediate setting, the condenser C6 is ini serted in series with the last active condenser to halve its effective magnitude. If it is desired to change capacity from zero to 10 mfds., for example, in steps of l mid., each of the condensers CI to C6 should have a value of two mfds.

For extending the range of capacity change which can be effected in the circuit connected to terminals T, TI, several arrangements such as shown in Fig. l0 may be connected in parallel, and preferably the values of capacity of the uits of the several sets will bear a decimal relation to each other.

For convenience, the term set appearing in the claims means a group of impeda-nces under the control of a common switching system, and the term box applies to two or more sets with connections.

What I claim is:

1. A resistance box comprising at least two units each comprising a rotatable structure, a plurality of resistors carried by said structure, a series of angularly spaced contacts mounted on said structure and connected to said resistors, and a terminal contact mounted on said structure; a stationary contact brush in continuous engagement with the terminal contact of one of said units, a stationary contact brush for successively engaging the angularly spaced'contacts of another of said units, and a stationary contact brush for engaging the terminal contact of one unit and for successively engaging the angularly spaced contacts of an adjacent unit.

2. A resistance box comprising at least two units each comprising rotatable structure, a plurality of resistors carried by said structure, a series of angularly spaced contacts mounted on said structure and connected to said resistances, and a terminal contact mounted on said structure; a stationary contact brush for engaging the terminal contact of one unit and for success`.vely engaging the angularly spaced contacts of an adjacent unit, a second contact brush for successively engaging the angularly spaced contacts of said adjacent unit, and a stationary auxiliary resistor connected between said contact brushes.

3. A resistance box comprising at least two units each comprising rotatable structure, a 'plurality of resistors carried by said structure, a series of angularly spaced contacts mounted on said structure and connected to said resistances, and a terminal contact mounted on said structure; terminal posts for said box, contact brushes for connecting said units in series, and means for minimizing inductive effects comprising conductors from one of said brushes to one of said binding posts, said conductors being disposed on opposite sides of at least one other of said brushes in which the current flow is opposite in direction to the current flow through said conductors.

4. A resistance box comprising at least two rotatable drums having parallel axes of rotation, a plurality of resistances of fixed and equal magnitude mounted on each of said drums and angularly spaced about the axis thereof, a plurality of angularly spaced contacts mounted at one end of each of said drums and connected to said resistances, a terminal contact mounted on said one end of each of said drums, and a contact brush for continuously engaging the terminal contact of one drum and for successively engaging the angularly spaced contacts of an adjacent drum.

5. A resistance box comprising at least two units each comprising a rotatable structure, a plurality of resistors of fixed magnitude carried by said structure, contacts mounted on said structure and connected to said resistors thereon, and a stationary brush connecting a predetermined contact of one of said rotatable structures selectively to any of the contacts of another rotatable structure.

6. A resistance box comprising a rotatable drum, a plurality of equal and serially-connected resistances carried thereby and rotatable therewith, angularly-spaced contacts carried by said drum and connected to said resistances, a pair of stationary contacts adapted to engage adjacent of said angularly spaced contacts for alternate settings of said drum and to engage the same contact for intermediate settings of said drum, and a stationary resistance equal in magnitude to each of the rotatable .resistances continuously v connected between said stationary contacts.

7. A resistance box comprising a rotatable drum, a plurality of equal, and serially-connected resistances carried thereby, angularly spaced contacts carried by said drum, a pair of stationary contacts for cooperating therewith, a stationary resistance equal in magnitude to each of said rotatable resistances connected between said stationary contacts, an index and scale coupled to said drum, and means for accurately arresting said drum upon relative movement of said index and scale inv one direction alternately in positions for which said stationary contacts engage adjacent contacts carried by said drum and in intermediate positions for which said stationary contacts engage one of said rotatable contacts whereby the resistance of the box is varied by steps each equal to one-half the magnitude of each of said resistances.

' 8. A resistance box comprising a movable indicating member indicating a number of resistance values differing progressively by equal increments for successive settings of said indicating member in one direction, a pair of contacts, a resistor continuously connected between said pair of contacts and of a magnitude twice the increment, a pluralityof resistors connected in series and each of the same magnitude as said first resistor, a plurality of contacts connected to said plurality of resistors, and means operable upon movement ot said indicating member to effect relative movement between said plurality of contacts and said pair of contacts, the dimensions and spacing of said contacts in the direction of movement being such and so related to movement of the indicating member that when said indicating member indicates even multiples of said increment said rst resistor is eiectively out of circuit and when said indicating`member indicates odd multiples of said increment said first resistor is in shunt to one of said plurality of resistors effectively in circuit. A LEO BEHR.

CERTIFICATE or coRREoTIoN.

Patent No. 2,005, 986. June z5. 193s.

LEo BEHR.

lt is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page 2, first column, line 72, for the patent number 11,992,499" read 1,972,499; and that the said Letters Patent should be read with this correction therein that the same may conform to the record of thc case in the Patent Office.

Signed and sealed this 16th day of Jul'y, A. D. 1935.,

Leslie Frazer (Seal) Acting Commissioner of Patents.

CERTINCATE or coRREcTloN.

Patent No. 2,005,986. June 2s. 193s.

LEO BEHR.

lt is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page 2, first column, line 72, for the patent number 11,992,499" read 1,972,499; and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 16th day of Jul'y, A. D. 1935...

Leslie Frazer (Seal) Acting Commissioner of Patents. 

